1. Field of the Invention
This invention relates to a wiper arm for an automotive windshield wiper system. More particularly, this invention relates to a wiper arm of the aforesaid character of unitary construction with a narrow, thickened free or distal end of a double thickness that is formed by hemming.
2. Description of the Prior Art
Typical prior art windshield wiper arm assemblies 10 used on motor vehicles as shown in FIGS. 1 through 5 normally consist of a mounting head 12, retainer arm 14 and wiper or arm rod 16, as well as, a tension or a coil spring 20. The mounting head 12 is typically manufactured of zinc or aluminum die cast. Typically the retainer arm 14 is formed from sheet metal and stamped in a general U-shaped configuration as shown in FIGS. 4 and 5. The windshield wiper arm assembly 10 also has a wiper blade (not shown), which has a support bracket system and wiper strip retainer (not shown). The wiper blade is pivotally connected to the windshield wiper arm assembly 10 through use of a hook like end 17 of the wiper rod 16 which engages between two lateral cheeks of the support bracket system of the wiper blade (not shown). The fit with the support bracket requires a sizing operation on the width of the hook like end 17 so that it will properly fit between the two lateral cheeks of the support bracket it engages. The connection thus formed guides the wiper blade with the wiper strip over the glass windshield of the motor vehicle. The jointed connection and the support bracket system make it possible for the wiper strip to adapt to a curvature of the windshield. A required contact pressure of the wiper strip on the vehicle windshield is attained with at least the tension coil of the spring 20 which braces the mounting head 12 and the retainer arm 14 in conjunction with the wiper rod 16 through a toggle joint 21.
The shape of the individual components of the retainer arm 14 is influenced by various demands and stresses. Specifically, they should be as torsionally rigid, deflection-resistant, and as narrow in the field of view as possible, so that the wiper blade can be guided without vibration and under control over the vehicle windshield yet present little hindrance to the field of view. The mounting head 12 transmits the drive moment from the drive axis A-A to the wiper blade, via the retainer arm 14 and the arm rod 16. It also forms part of the toggle joint 21, by way of which the mounting head 12 is braced with the retainer arm 14 by the tension spring 20 and pressed in the direction of the vehicle window. The greatest forces or moments arise in the mounting head 12, both parallel to the window and perpendicular to the window. Further, deformations in the lower region of the retainer arm 14 have an especially strong effect over the entire length and can cause uneven wiping speeds as a result of a spring effect. The mounting head 12 and the first portion of the retainer arm 14 must therefore be embodied as especially deflection-resistant and torsion-resistant.
In a wiping motion, the outward portion of the retainer arm 14 moves partly, and the wiper or arm rod 16 moves completely, through the field of view of the driver and as a result they must be made not only torsion and deflection resistant, but also especially narrow so that they impede as little of the driver's view as possible. Further, the retainer arm 14 should be shaped in such a way that it is not lifted away from the vehicle window by the air flow across the windshield.
To accommodate these various requirements, prior art windshield wiper arm assemblies 10 have a wide mounting head that may be made of zinc or aluminum die cast or sheet metal as well as a retainer arm 14 that is also made of sheet metal which is relatively wide in the region of the mounting head 12 that is, at the lower edge 22 of the field of view of the driver. Often, this portion of the retainer arm 14 is made with an inverted U-profile that is open towards the window as shown in FIG. 5. Such profile has a relatively strong resistance moment, and is especially torsion and deflection resistant in this area while also being able to accommodate the tension spring 20 which is concealed in the U-profile. In the outward direction towards the free arm end of the retainer arm 14 where the retainer arm 14 connects with the wiper rod 16, the retainer arm 14 tapers so that it is narrower in the field of view of the driver as shown in the cross-section of FIG. 3. Over the full length of the retainer arm 14, the profile has a constant material thickness, determined by the sheet metal thickness used. This thickness is designed in order to accomplish the appropriate dimensional stability under the greatest material stresses to be expected which are basically bending and torsion stresses, specifically, perpendicular and parallel to the vehicle window.
Generally, the wiper rod 16 is formed of a profile of constant thickness material solid flat stock, which is either crimped or riveted 30 as shown in FIGS. 1 and 3 to the retainer arm 14. The thickness of the wiper rod 16 is a function of drive and contact forces, the length of the retainer arm 14, as well as the resistant moments to the windshield wiper arm assembly 10. Further considerations are the effect of wind engagement faces as well and more importantly, the slender structure in the field of view of the driver. Generally, the material stress demands are greatest at the connection point of the wiper rod 16 to the retainer arm 14 and because of the small cross-sectional area and unfavorable resistance moments, the material thickness is generally determined by the stress requirement at the connection point between the retainer arm 14 and the wiper rod 16. For this reason, the wiper rod 16 itself is generally a solid stock formed of a thicker material than the retainer arm 14 thus, the arm rod 16 and retainer arm 14 are combined in a single rigid assembly which rotates a limited degree about drive axis A-A. As a result, in some applications, there is unnecessarily high consumption of material, high material costs, and high weight.
Further considerations to be made in the design of a complete windshield wiper system is the associated windshield washing system and considerations which need to be made with respect to the mounting of the spraying device on the hood or the windshield wiper arm assembly 10. The windshield washing system consists of a washing liquid reservoir, as well as a pump (not shown), by which washing liquid is sprayed onto the windshield to be cleaned by a spraying device. It is known that the spraying device may be stationarily arranged on the engine compartment hood. Further, the windshield cleaning system-spraying device maybe fixed to the windshield wiper arm assembly 10. The advantage of fixing the spraying device to the windshield wiper arm assembly 10 is that the washing liquid is sprayed immediately in front of the wiper blade. In the prior art embodiment illustrated in FIGS. 1 through 5, the mounting bracket 26 for attaching a spraying or washer nozzle 28 is riveted to one of the legs of the U-shaped retainer arm 14. In some prior art embodiments the mounting bracket 26 may be stamped out of the profile of the U-shaped leg of the retainer arm 14 and laterally spaced with respect to the plane of the leg of the U-shaped retainer arm 14. This attached structure provides a very stabile, rigid mounting surface for the spraying nozzle 28 which provides an attractive, compact assembly in which the fluid line or hose 24 can be dressed substantially entirely within the cavity of the U-shaped retainer arm 14 and thereby be out of sight from the user.
With reference to prior art FIG. 2, the details of the spraying or washer nozzle 28 are illustrated. The washer nozzle 28 includes a body portion and a mounting flange integrally formed therewith for mounting washer nozzle 28 with mounting bracket 26. The fluid line 24 is connected to an inlet nipple to provide washer fluid to an inlet port. As a result, a spray or mist is expelled from a nozzle port of the outlet nipple.
In order to solve high cost and high weight problems, some windshield wiper assemblies particularly teach the use of a retainer arm and wiper rod which can be made of a number of variable material layers which are folded upon one another in various regions until the material thickness required for the particular cross-section is obtained. A thin material is bent over multiple times by approximately 180° in multiple steps in order to brace each layer. The advantage, of course, is from a relatively thin sheet of metal, different material thickness can be obtained in different regions and this thickness can be adapted exactly to different stresses that arise. Unfortunately, small material stress cracks, virtually invisible to the eye, can result from these multiple bending operations and as a result, such minute cracks, if they occur on the outer surfaces, can cause excessive noise by wind passing thereover when exposed to a high wind stream. Further, obviously, the multiple layers of metal in order to accomplish the appropriate size requirements, may also result in higher material costs as well as higher weights due to the multiple layers which are necessary in order to provide the appropriate structural rigidity for the torsion and deflection forces that are known in selective areas of the windshield wiper assembly. Generally, to enable the use of multiple layer assemblies, a thinner material is used in order to make the multiple folds which are necessary to acquire the particular cross-section needed to resist the known deflection and torsion moments.
U.S. Pat. No. 6,505,377 B1 (Merkel et al.) discloses a wiper arm or wiper rod, element 18, for a windshield wiper assembly, the wiper rod being formed from multiple layers of a single thickness component sheet of metal (column 2, lines 30-39). The free or distal end of a one-piece wiper rod according to this reference is formed with four thicknesses of metal by a stamping operation, FIG. 8, presumably to provide the wiper rod with adequate stiffness to resist deflection or tension stresses under aerodynamic load, to thereby maintain a wiper blade that is attached to the free end in contact with an adjacent windshield and without requiring an excessive wiper rod width at the outer region, which is in the field of vision of an operator of the associated motor vehicle. A known problem with the FIG. 8 configuration of the wiper arm or rod of this reference is that the number of bends as a result of stamping of the metal strip in order to achieve this configuration, requiring a 180° bend at the location of the lower detent holes (elements 56), in addition to four 90° bends to achieve such configuration, can introduce cracking in outer surface layers of the metal. Such surface configuration is undesirable because it can lead to excessive noise in the associated vehicle when the vehicle is traveling at highway speeds.
The '377 reference also discloses an alternative embodiment, the embodiment of FIGS. 9-16, in which the free or distal end of the wiper rod is formed by a stamping operation in a triple thickness, as shown in FIG. 14, which also requires severe bends on each of the ends of the blank from which the rod is formed, following a 90° bend in advance of each 180° bend. The FIG. 14 embodiment of the invention of the '377 reference, of necessity, will require a thickness sufficient to accommodate three (3) layers of material, and it will require extra width of the blank from which the wiper rod is formed to provide this triple thickness construction. The multiple layer assembly is not cost effective because of the additional processing steps to generate the various bends and the resultant higher weight due to the multiple layers of metal.
U.S. Pat. No. 6,732,401 B1 (Rapp), which shows an assignment to the same assignee as the '377 patent, shows, in FIGS. 3 and 5, a wiper arm assembly in which the free end has an open or box type cross-section, presumably for added rigidity in this region. The use of a box-type configuration in this region adds to the required thickness of the rod or arm at a location in the field of view of the driver, which, at the least, serves as an annoyance to the driver and is, in any case, aesthetically unattractive. Again, such configuration is not economical and requires additional processing steps to obtain the various material thickness configuration of the hook like end 21.